Two-layer mattress spring unit



FIG. 1 is a perspective view of the two-layer mattress spring unit, the shading illustrating contrasting tones between an upper layer and a lower layer of the two-layer mattress spring unit;

FIG. 2 is a right side view thereof, the left side view being a mirror image of the right side view;

FIG. 3 is a front view thereof, the rear view being identical to the front view;

FIG. 4 is a top view thereof; and,

FIG. 5 is a bottom view thereof. 

CLAIM The ornamental design for a two-layer mattress spring unit, as shown and described. 